My seventh Advent Policy Brief falls on my birthday :), so excuse my superficiality in this short brief. Final grades should only have three outcomes: pass, fail, and commendation.
Education imparts skills and shares knowledge. At the end of instruction, the pupil either has the taught skill/knowledge or does not. And if they do, they either practice it with mastery, or they do not. I'm not saying don't give people number-or-letter-graded tests and assignments, but there are two hard lines at the points of competence and excellence.
When it's a numbers game, the wallet always wins. Parents with resources better prepare their children to achieve high performance averages than parents without resources. Public schools are accused of inflating grades in effort to see their best students compete with elite private school college applicants.
Numerating performance creates competition instead of cooperation; this dynamic drags down our brightest. The difference between a 90% and a 99% is an existential chasm for a Tracy Flick or Randall Pearson. Many teen dramas have shown how much stress, time, and money is dedicated to valedictorian and college applications.
A commendation ought to hold a degree of prestige as proof mastery over course material. Students may be exceptional by talent or by effort or by opportunity. We need to stop pitting exceptional people against each other.
The purpose of education is not to assign you a score that takes you to your "correct place" in the economy.